A troublesome set of traffic lights near the junction for South Mimms and the A1(M) are sometimes manipulated intentionally, the WHT has learnt.

Motorists using Junction 23 of the M25, approaching from St Albans Road (A1081), have sometimes been left frustrated because of what they perceived to be faulty traffic lights only staying green for a few seconds.

However, a Highways England spokesman told the WHT that it occasionally tweaks the settings in an attempt to ease congestion on the roundabout – aiming to prevent queuing traffic on the M25 exit slip road.

Instead, the adjustment causes long tailbacks towards Barnet – but crucially on the less-busy A1081, rather than the anticlockwise carriageway back to Potters Bar.

The lights have also been prone to malfunctioning, but the spokesman said they are only intentionally manipulated when there is heavy M25 congestion.